But PayPal faces threats from larger tech companies though. Amazon(AMZN), Apple(AAPL) and Google(GOOGL) are all trying to make waves in the digital payments business.

PayPal CEO Dan Schulman said in an interview with CNNI's Maggie Lake Monday morning that competition is growing.

But he thinks PayPal stands out because it truly is an independent middleman. Unlike Amazon, Apple or Google, it's not part of some larger entity.

"Probably the biggest advantage we have is we're truly a neutral third party," Schulman said. "We can work with any merchant, any platforms -- whether that be iOS, Android or Windows -- and provide a seamless, consistent experience for consumers and merchants."

Schulman added that he thinks PayPal stands to benefit as more and more consumers use their mobile phones to pay for things in actual stores -- in addition to using the PayPal online site or app for mobile purchases.

"Last year, we did over 1 billion mobile payment transactions," he said.

Still, there's also a hot private startup called Stripe that PayPal and its investors will have to watch closely. Stripe is backed by PayPal co-founders Max Levchin and Peter Thiel -- as well as Musk.

So it's telling that Musk and these other PayPal veterans are investing in something that competes against the company they started.